1. Field of the Invention
The present invention relates to a pulse sequence in Magnetic Resonance Imaging (MRI), and particularly to a method and an apparatus for calibrating an MRI pulse sequence.
2. Description of the Prior Art
An imaging sequence in MRI, particularly fast sequences, sometimes can be affected by a system's imperfect performance, such as eddy currents, insufficient radio frequency power, etc., and the system's physical characteristics, such as RF penetration in a high field strength MRI system. In a high field strength MRI system, the RF penetration can induce phase jumping, thereby leading to errors in phase calibration, which in turn leads to unclear images and the generation of imaging artifacts.
Referring to FIG. 1, a current method for performing phase calibration on scanned data includes the following steps:
step 10: acquiring scanned data and entering the scanned data into k-space;
step 20: reading out the scanned data line-by-line from k-space and obtained the Fourier transformation thereof;
step 30: performing phase calibration on the data obtained by the transformation; wherein the phase calibration includes a constant phase calibration and a linear phase calibration;
step 40: Fourier transforming the phase-calibrated data; and
step 50: reconstructing an image using the phased-calibrated data.
In a practical conventional system, a common practice is to perform the calibration only to the linear phase and usually a calibration to the constant phase is skipped. However, since the phase jumping induced by the RF penetration mainly results in errors in the constant phase, it is necessary to perform calibration to the constant phase.